This disclosure relates to acoustic downhole measurements and, more particularly, a differential energy analysis of dipole acoustic signals to facilitate identification of geological or borehole characteristics.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as an admission of any kind.
Acoustic measurements may be used to evaluate a borehole in a geological formation. Generally speaking, acoustic downhole tools may use monopole or dipole acoustic transmitters to obtain acoustic measurements. A monopole transmitter emits energy equally in omni-direction away from its center, while a dipole transmitter emits energy in a particular direction. To identify fractures in a borehole, monopole transmitters may be used in what is referred to as a low frequency Stoneley waveform analysis. Specifically, a Stoneley wave propagates along the interface between the borehole fluid and the formation. Thus, the monopole low frequency acoustic signal may attenuate depending on characteristics of the geological formation along the borehole, such as a fracture or permeable zone. Accordingly, monopole Stoneley waveform analysis may be a useful tool to identify fracture or permeable zones in a borehole.
The monopole Stoneley waveform analysis, however, may also be affected by other borehole characteristics other than the presence of fractured zone. Borehole enlargements and/or bed boundaries, from the perspective of a Stoneley waveform analysis, could have similar signatures to a highly fractured zone. As such, it may be difficult to differentiate a highly fractured zone from a problematic rugose borehole using a Stoneley analysis alone. To differentiate these different situations, a borehole image may be obtained and compared to the Stoneley waveform analysis. However, there may be situations in which a borehole image is not available.